Matilda loves science and inventing. Her heroes are Marie Curie, Leonardo da Vinci and Thomas Edison, and one day she wants to be a famous inventor herself. So when she doesn't win the school science fair, she's devastated - especially as the judges didn't believe she'd come up with her entry on her own. Because she's a girl.

When Matilda shares her woes with her Grandma Joss, she's astonished to learn her grandma was once a scientist herself - an astrophysicist, who discovered her very own planet. Trouble is, Grandma Joss was also overlooked - her boss, Professor Smocks, stole her discovery for himself. And he's about to be presented with a Nobel Prize.

Matilda concocts a plan. They'll crash the award ceremony and tell everyone the truth! So begins a race against time - and against Matilda's strict mum and dad! - on a journey through Paris, Hamburg and Stockholm, and on which they encounter a famous film star, a circus, and a wanted diamond thief...